1. Field of the Invention
The present invention relates to a rotating blade body, which is mounted to a rotary machine such as a turbine part of a gas turbine, steam turbine, jet engine and the like or an air compressor of a gas turbine and jet engine and rotates with a main shaft in an integrated manner, and relates to a rotary machine to which a rotating blade body is installed.
2. Description of the Prior Art
Generally, in a rotary machine such as a turbine part of a gas turbine and the like and an air compressor, a main shaft is installed inside a casing constructing an outer shape so as to achieve axial rotation. Rotor discs are installed to this main shaft in a plurality number of stagesaxially, and a plurality number of pieces of rotating blades are extending from the outer circumference of each of rotor discs in a radial pattern. These rotor discs and rotating blades constitute a rotating blade body, which rotates together with the main shaft in an integrated manner. Additionally, stationary vanes are installed to the casing along the main shaft so as to be arranged in a manner of alternating with the rotating blades.
In a case of a gas turbine, in a turbine part constructed as described above, high temperature and high pressure combustion gas is supplied from a combustor, and by having this combustion gas flow by way of rotating blades and stationary vanes alternately, the main shaft is rotary driven together with rotating blades, namely with a rotating blade body. Then, when a generator is connected to an edge of the main shaft, turning force of the main shaft is utilized as a source of electric power generation. On the contrary, when an engine nozzle for exhaust of combustion gas is installed at an end of the turbine part, turning force of the main shaft is utilized as a jet engine. In a case of a steam turbine, by having high pressure steam flow by way of rotating blades and stationary vanes alternately, the main shaft is rotary driven, and turning force of this main shaft is utilized as a source of electric power generation of a generator.
On the other hand, in an air compressor of a gas turbine, a rotating blade body rotates together with a main shaft by rotation of the main shaft. By this, the air is inhaled from the outside and supplied to a combustor, being compressed by way of rotating blades and stationary vanes alternately. Here, compressed air being introduced into a combustor is burned with fuel being supplied, resulting in high temperature and high pressure combustion gas, which is to be supplied to a turbine part of the above-mentioned gas turbine.
Here, a rotating blade body consists of a rotor disc and rotating blades that are manufactured independently and is constructed in a manner that the rotating blades are assembled to the rotor disc. To be more precise, as shown in FIG. 14 and FIG. 15, a rotating blade 1 mainly has a blade root portion 10 whose vertical section is formed in a Christmas tree, a profile portion 11 and a shroud portion (not illustrated herein).
A blade root portion 10 is a portion which is to be engaged to an after-mentioned blade groove 20 in a rotor disc 2, functioning to maintain a rotating blade against the rotor disc 2. A profile portion 11 is a portion which has a transverse section shaped in a streamline and extends by being gradually twisted while maintaining this streamlined shape, and it functions so as to make fluid such as combustion gas, high pressure steam and air flow substantially in a smooth manner. A shroud portion is a portion which has a transverse section shaped approximately in a letter “Z” and is formed on an edge of a profile portion 11, and when a rotating blade body rotates at a high speed together with a main shaft, the end face of each of shroud portions of rotating blades 1 neighboring each other comes to contact with each other, by slightly decreasing the twisting degree of the profile portion 11 due to a centrifugal force being applied, and as a result, a shroud portion functions so as to stabilize the circumferential arrangement of the rotating blades 1 as a whole.
On the other hand, on an edge of the outer circumference of a rotor disc 2, blade grooves 20 being shaped approximately the same as longitudinal section of blade root portions 10 of the rotating blades 1 are formed at regular intervals in a circumferential direction along a rotating shaft. Into each of these blade grooves 20, blade root portions 10 of the rotating blades 1 are inserted from a direction of the rotating shaft and engaged. In this way, the rotating blades 1 are assembled to the rotor disc 2 so as to obtain a rotating blade body in which a plurality number of pieces of rotating blades 1 extend from an outer circumference of the rotor disc 2 in a radial pattern.
Especially, in a case of a rotating blade body which is to be installed to a turbine part of a gas turbine and the like, due to exposure to very high temperature, only the bottom portions 20a of the blade grooves 20 of the rotor disc 2 are widened largely for the bottom-end portions 10a of the blade roots 10 of the rotating blades 1, in order to restrain an excessive increase in temperature of a rotating blade body itself caused by the aforementioned exposure. In other words, between the bottom-end portions 10a of the rotating blade roots 10 and the bottom portions 20a of the blade grooves 20, circulation spaces 25 for cooling air are formed along a direction of a rotating shaft, having the cooling air for cooling the rotating blade body circulate through these circulation spaces 25.
Also, between the blade root 10 and the blade groove 20, except in this circulation space 25, generally a slight gap of approximately 0.1 mm width exists, considering easiness of insertion and extraction, maintaining integrity of post-assembly position. Therefore, the rotating blades 1 are in such a condition as to be able to move or incline toward the rotor disc 2 slightly.
And now, during steady-state operation of a turbine part of a gas turbine and the like and an air compressor to which such a rotating blade body as described above is installed, the main shaft rotates at a high speed. Therefore, a high centrifugal force which is high enough to substantially neglect gravity of empty weight acts on the rotating blades 1 that rotate at a high speed together with the main shaft. As a result, the rotating blades 1 are bound so as to always come up, facing outward in a radial direction against the rotor disc 2. Consequently, movement or inclination of the rotating blades 1 toward the rotor disc 2 does not occur, but each of the rotating blades 1 is secured in a predetermined position, being well-balanced as a whole of a rotating blade body.
However, at a time of start-up of operation or at a time of shutdown, or during a preliminary operation, because the main shaft rotates at a low speed, the rotating blades 1 which rotate together with the main shaft do not have so high centrifugal force act on them. Therefore, the rotating blades 1 being in progress of rotation move inward in a radial direction (downward in a vertical direction) of the rotor disc 2 by action of the gravity of empty weight when the rotating blades 1 are located on the upper side in a direction perpendicular to the rotating shaft. On the contrary, when the rotating blades 1 are located on the lower side in a direction perpendicular to the rotating shaft, the rotating blades 1 are momentarily placed in a condition that they have moved outward in a radial direction (downward in a vertical direction) of the rotor disc 2. In a process of making transition to these conditions alternately, the rotating blades 1 come to incline repeatedly toward the rotor disc 2 in a circumferential direction due to an action of moment of the gravity of empty weight.
Then, because local impact of blade roots 10 occurs repeatedly in blade grooves 20 as a result of these repeating movement and inclination of the rotating blades 1, local wear and deformation are caused in the blade grooves 20 and at the blade roots 10. In addition, because the position of the center of gravity of the rotating blade body itself varies repeatedly so as to cause unbalancing to the rotating blade body, inadvertent vibration is induced. Furthermore, when local wear and deformation make a progress excessively in the blade grooves 20 and at the blade roots 10, an amount of movement or an amount of inclination of the rotating blades 1 becomes larger at a time of start-up and the like when the main shaft rotates at a low speed, so that further unbalancing is caused to the rotating blade body, resulting in higher vibration induced by this unbalancing. Additionally, during a steady-state operation, because each of the rotating blades 1 is secured at a position drifting from the predetermined position, the position of the center of gravity of the rotating blade body itself varies, resulting in occurrence of inadvertent vibration.
In order to solve the above-mentioned problem, as a conventional technique as disclosed in the Japanese Utility Model Application Laid-Open H4-119392, a rotating blade body has leaf spring pieces being curved in a wave pattern in the direction of the rotating shaft inserted so as to be engaged into gaps between the bottom-end portions 10a of the blade root portions 10 and the bottom portions 20a of the blade grooves 20. In this rotating blade body, the rotating blades 1 are pressed up outward in a radial direction against the rotor disc 2, by receiving a snapping force from the leaf spring pieces and resisting against the gravity of empty load and a moment thereof, and as a result, are placed in a condition to be steadily secured at a same predetermined position as during steady-state operation. Therefore, during start-up operation and the like, the rotating blades 1 are restrained from moving and inclining. As a result, it is possible to prevent the blade grooves 20 and the blade roots 10 from being subject to local wear and deformation and inadvertent vibration may not occur.
However, while the above-mentioned improvement technique is effective for a rotating blade body in which gaps between the bottom-end portions 10a of the blade roots 10 and the bottom portions 20a of the blade grooves 20 are not so large, such as a rotating blade body for an air compressor of a gas turbine, for example, which normally does not require a circulation space 25 for the cooling air, on the contrary, it is not necessarily effective for a rotating blade body for a turbine part of a gas turbine which requires securing of a circulation space 25.
First, it is because when the gaps between the bottom-end portions 10a of the blade roots 10 and the bottom portions 20a of the blade grooves 20 are larger, the degree of curving in a wave pattern of the leaf spring pieces is restricted substantially, which deteriorates the snapping force contributing to pushing up of the rotating blades 1. As a result, the rotating blades 1 are not secured in a predetermined position against the rotor disc 2 sufficiently on a steady basis, causing movement and inclination of the rotating blades 1 substantially. As a result, inadvertent vibration occurs with local wear and deformation. Secondly, it is because circulation of the cooling air inside the circulation space 25 is disturbed widely by the leaf spring pieces and as a result, cooling efficiency of a rotating blade body is deteriorated.